The present invention relates to a slide-type exhaust braking system intended to apply a braking function to a vehicle by blockading a passageway for an exhaust gas on the occasion of a sharp downward slope, this braking system being connectively interposed in an exhaust pipe generally in large-sized vehicles such as a track, a bus or the like.
2. Description of the Prior Art
FIG. 4 is a partially cut-away view illustrating the principal portion in section of a prior art exhaust braking system of this type. The system is, as shown in the Figure, arranged such that: a body housing (21) of the exhaust braking system is formed with an internal exhaust passageway (22) and a reciprocation passageway (23) appropriated to a tabular valve member (24), this reciprocation passageway (23) communicating with the exhaust passageway (22) so as to extend in the direction substantially orthogonal to this passageway (22); in the reciprocation passageway (24) the valve member (24) includes an exhaust pressure adjusting hole (25) consisting of a slot which is so formed in the bottom portion in front thereof as to lead to the rear passageway, the valve member (24) being loosely engaged with a portion vicinal to the tip of a piston rod (26) projecting on the side of an actuator device (not illustrated) with the help of an upper retaining groove wall (24') provided in the front thereof; a middle pressure receiving member is pressed by the tip of the piston rod (26); an inducement wall member (27) is mounted on the piston rod (26) which is positioned between the retaining groove wall (24') and the pressure receiving wall (24") to engage with the retaining groove wall (24') when the exhaust passageway is opened by the valve member (24); an auxiliary valve member (28) mounted on the inducement wall member (27) slides on the surface of the valve member (24) upon a press against the middle pressure receiving wall (24") when the exhaust passageway (22) is closed by the valve member (24), thereby closing the exhaust pressure adjusting hole (25); when the exhaust passageway is opened, the auxiliary valve member (28) slides to open the exhaust pressure adjusting hole (25) following the engagement with the retaining groove wall (24') with the movement of the piston rod (26) prior to the step of opening the exhaust passageway, with the result that the exhaust gas stagnant in the front portion partially escapes through the exhaust pressure adjusting hole (25) toward the rear passageway; and the exhaust pressure appiled to the valve member (24) is thus decreased.
There arise, however, some problems inherent in the conventional exhaust braking system. Namely, deterioration in mechanical strength is caused in the valve member (24) because of a structure of the exhaust pressure adjusting hole (25) consisting of the slot penetrating the bottom in front of the valve member (24). Friction damages and abrasion are created on the friction surface between the auxiliary valve member (28) and the surface in the vicinity of the exhaust pressure adJusting hole (25) of the valve member on account of opening/closing operations of the valve member (24) which are repeated with high frequency during the operation of the system. A decline in close engagement between the two members continues to be produced for a long stretch of time, whereby the braking function is forced to decrease.